Trump loves to fight — especially on Twitter.

You can see clear proof of Trump's inability to let things go if you look at his Twitter feed. The Hollywood Reporter compiled a list of 20 of the best Trump twitter fights — published in 2013, long before Trump was running for office. He's only gotten worse.

DeGeneres really wasn't far off when she called Trump a bully, and Cooper wasn't off when he called Trump a five-year-old: the nominee proves it almost every day with juvenile statements and tweets. In fact, DeGeneres should probably expect an angry tweet from Trump soon.

You can watch the full clip of the Nightline interview with Ellen DeGeneres below.